People have stated that the percentage of vandalism by anonymous users has gone up recently.

Is this simply because we have instituted IP blocking, and increasingly use it?

It's hardly unlikely. In fact, it's what normally happens when hard security measures are taken.

Surely you mean to say "logged in users" at the end of the first line? Then yes, this is what happens when people meet with hard security, they find ways to work around it.

-- Toby